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Old 07-25-2010, 06:44 AM
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Another vac and timing question ?

I know this has been beaten, battered and hammered to death but I just want to make sure I get it.

From the information my mind has absorbed ( sometimes it misses quite a bit ) The total timing "magic Number " does not exist. 32 - 36 deg. is a good place to start @ 3000 rpm. Depending on the light being used ( mine is almost 30 yrs. old ) From there, optimum performance could be more or less, depending on the engine. Is that accurate?


Next, My summit carb directions tell me to use the "timed spark port" for the dist. advance pg.5 From what I have read here (hotrodders), it should be hooked to the manifold direct. The carb does have a full manifold port but my TH 400 likes it. Can I split it to run both the Trans. and Vac adv.? or should I grab something right out of the manifold? It has been running good the way I have it but I am now trying to get the most out of it and want to start from square one.

Thank you for being patient with me.


Last edited by Fast 4 Door; 07-25-2010 at 06:53 AM.
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Old 07-25-2010, 07:50 AM
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Well to help you with my experience I hooked my vacuum advance canister up to full manifold vacuum and it helped me with my current setup I have but I am running a bigger cam with 222/230 @ 50 duration and running 16 degrees initial and with vacuum advance hooked up to full manifold it gives me 16 degrees of extra advance at idle and helps my idle to be cleaner and engine run better idle wise. Used to run timed port and off idle wise there is no difference in engine performance wise between full and timed for my setup anyways. Just works really nice at idle which is where it helps.

From reading articles once you have the gas pedal down there is no difference between timed and full manifold since the timed port will now give full vacuum signal since your butterfly's are now open.

Also I am running a turbo 350 and I just put a T into the line to my vacuum modulator and I have had no issues and vacuum advance works no problem.

I am getting ready to put a smaller cam in though (212/218 @ 50) and I will have to see how it does but from what I have read full manifold vacuum is what more people use for bigger cams and even stock type cams just depends on how the engine will work with it and also how much vacuum advance degrees your canister gives.

I have an adjustable one and the lowest it will give is 16 degrees so I got an Accell one which will give me more adjustment. So hook yours up if its adjustable and see how it does. I will have mine set up to give me only about 12 degrees of vacuum advance since I run a lot more timing at idle.
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